Night-time solar energy could power satellites

January 21, 2026

From shimmering coastlines to sun-drenched deserts, sunlight is woven into Australia’s national identity. In Sydney, however, researchers are rethinking how solar energy works — not by capturing sunlight during the day, but by generating electricity after dark.

At the University of New South Wales (UNSW), scientists are developing a new kind of energy technology that works in reverse to traditional solar panels.

“We’re creating devices that produce electricity by emitting light, rather than absorbing it,” explains Jamie Harrison, a postgraduate researcher at UNSW. “You can think of it as a reverse solar cell.”

Turning earth’s heat into electricity

Harrison is part of a research group at UNSW’s School of Photovoltaic and Renewable Energy Engineering exploring innovative ways to harvest solar energy — even when the sun is no longer visible.

During daylight hours, the Earth absorbs heat from the sun. At night, that stored energy is released back into space as infrared radiation, a form of light invisible to the human eye but experienced as warmth. The UNSW team is working with a semiconductor device known as a thermoradiative diode, which can convert this infrared radiation into usable electrical power.

“If you observe the planet with an infrared camera at night, you’d see the Earth glowing,” says Professor Ned Ekins-Daukes, who leads the project. “That glow represents heat being radiated into the cold vacuum of space.”

A first-of-its-kind power demonstration

While thermoradiative diodes had been theorized and explored by researchers at Harvard and Stanford, the UNSW team achieved a global first in 2022 by directly generating electrical power from the device.

At present, the output is modest — roughly 100,000 times weaker than a conventional solar panel.

“It produces about enough energy to run a digital wristwatch using body heat,” Ekins-Daukes notes. “The power depends entirely on the temperature difference between the heat source and its surroundings.”

Even under ideal conditions on Earth, thermoradiative diodes could only deliver about one watt per square meter, largely due to atmospheric gases like water vapor and carbon dioxide, which trap heat and reduce thermal contrast.

Why space is the real opportunity

According to Ekins-Daukes, the technology’s greatest promise lies beyond Earth’s atmosphere. In space, where extreme cold provides a perfect heat sink, thermoradiative diodes could operate far more efficiently.

One potential application is satellite power generation. Satellites currently rely on solar panels, which only function when exposed to sunlight.

“In low Earth orbit, satellites typically alternate between 45 minutes of sunlight and 45 minutes of darkness,” Ekins-Daukes explains. “Solar panels are useless half the time.”

Thermoradiative diodes could provide auxiliary power during those dark periods by converting heat absorbed earlier into electricity as the spacecraft cools in space. This would reduce dependence on onboard batteries, which must be charged during sunlight hours.

With the trend toward smaller, lighter satellites in lower orbits, Ekins-Daukes believes the diodes could be especially valuable.

“They’re lightweight, compact, and can generate power from otherwise unused surfaces,” he says.

The UNSW team plans to conduct a high-altitude balloon test flight later this year, marking the technology’s first real-world space-like trial.

Deep space applications and NASA research

Dr. Geoffrey Landis, a researcher at NASA’s John Glenn Research Center, says thermoradiative diodes could work in low Earth orbit — but only if manufacturing costs are kept extremely low.

“Batteries are inexpensive,” Landis points out. “For short periods of darkness, it’s usually cheaper to rely on batteries alone.”

Instead, NASA researchers are focusing on deep-space missions, such as probes traveling to the outer planets or rovers operating in permanently shadowed regions of the Moon.

These missions currently depend on radioisotope thermoelectric generators (RTGs), which convert heat from radioactive decay — often plutonium — into electricity. While effective, RTGs are heavy, expensive, and rely on scarce nuclear materials.

“They weigh around 45 kilograms, occupy significant volume, and are reserved for major missions,” says Dr. Stephen Polly, a NASA scientist collaborating with Landis.

Thermoradiative diodes could offer a simpler alternative. Multiple small diodes could be linked into panels resembling modern solar arrays, radiating waste heat as light while generating electricity more efficiently.

Engineering challenges and future outlook

Today’s thermoradiative diodes are made from semiconductor materials commonly used in night-vision equipment. However, researchers still need to evaluate how these materials perform under extreme temperatures produced by radioactive heat sources.

Traditional space-based thermoelectric systems operate at temperatures exceeding 1,000°C, raising concerns about durability and lifespan.

“For long-term missions, we need these materials to last decades,” Landis explains.

NASA teams are now testing new materials capable of operating reliably at temperatures up to 375°C. If development continues successfully, thermoradiative power systems could be mission-ready within five to ten years.

Back in Australia, the UNSW team has secured funding from the U.S. Air Force to further improve efficiency for low-Earth-orbit satellites. They are also experimenting with materials used in standard solar cells, which could allow thermoradiative diodes to be manufactured using existing production lines.

“That would let us scale quickly once the technology is commercially viable,” says Ekins-Daukes — a milestone he hopes to reach within the next five years.